Many off-road vehicles or heavy machines such as tractors, excavators, trucks, utilize a hydraulic system to accomplish power transmission for traveling or other heavy duty operations, e.g. operation of hydraulic rams and transmissions. Hydraulic fluid is significant to the performance of the hydraulic system as it is a power transmission medium, a lubricant of the hydraulic system, a heat-transfer medium and even a sealant in some situations.
Being the storage mechanism for the hydraulic fluid, it is desirable for the hydraulic fluid reservoir to provide the hydraulic system and, particularly, the hydraulic pump with hydraulic fluid of good quality that is free of particles and entrained air. Entrained air and particles will affect the performance and operability of various components of the hydraulic system such as the hydraulic pump. Due to operating conditions, the hydraulic fluid reservoir is often required to be capable of removing the particles and entrained air from the return flow.
A return filter and diffusing baffle have been adopted in hydraulic fluid reservoir design to remove particles and entrained air in the hydraulic fluid. However, when a considerably large flow is pumped through the suction port of the hydraulic fluid reservoir, the suction pressure may significantly reduce. This reduction in suction pressure can cause two types of cavitation. First, the gaseous type of cavitation is based on the release of the air dissolved in the fluid. Second, the liquid vaporization type of cavitation is based on the vaporization of the hydraulic fluid. This cavitation may cause a severe loss of pump efficiency and further reduce its service life due to cavitation wear. Therefore, a pressurized hydraulic fluid reservoir may be needed in order to deal with above situations and prevent undesirable pressure drops at the suction port and thus the inlet of a pump.
A prevailing technology for pressurizing fluid in the reservoir is to pressurize the air inside the reservoir. This pressure can be set following the ideal gas law. However, this technology demands the hydraulic fluid reservoir have more space to accommodate and manipulate the air pressure. Also, this technology exposes the fluid to more pressurized air, which will cause the hydraulic fluid in the reservoir to entrain more air and other impurities. Additionally, the air pressure will fluctuate when the hydraulic fluid inside the reservoir is at a drawn down level, such as, for example, upon displacement of a hydraulic cylinder.
The present invention provides improvements in hydraulic fluid storage reservoirs to provide a sufficient suction pressure at a high flow rate without increasing the storage volume and amount of entrained air in the fluid.